Stress is a commonly used word. But what does it really mean?
And why does a “stressy” horse have long term physical problems and lack resilience?
A stressed horse is not only an agitated or anxious animal: stress is much more than just that.
One could define stress as the sum of biological reactions to aggressive threats. This aggression can be external: perceived by the senses, internal (pain) or psychological (anguish, tension or worry). One distinguishes two types of stress:
1) physical stress (work, wounds, vaccinations)
2) psychological stress (anxiety, weaning, frequent transportation, change of environment, lack of turn out…)
Like humans, for horses there is a strong link between mind and body. This will be particularly noticeable in a situation of brutal conflict.
When the horse becomes anxious or scared (psychological stress), he may react in the following ways:
•widening of the eyes, heightening of respiratory rhythm, cardiac rhythm and blood pressure
•slowing of digestion (physical stress, sympathetic nervous system)
•maximal alertness, flight reflex.
When the situation returns to normal, the organism (using the parasympathetic nervous system) re-balances itself: regular respiratory and cardiac rates etc. are resumed. Physiological mechanisms permit body homeostasis. If the horse is stressed for too long or too frequently homeostasis could be permanently disrupted and trigger immunity troubles, sickness, wounds and fatigue.
Physical consequences of stress
*limbic system: centre for emotions, behaviour and memory.
*hypothalamus: regulation of homeostasis in coordination with the:
*pituitary gland: humoral responses.
As soon as a horse is affected by psychological stress the limbic system sends signals to the hypothalamus which in turn stimulates the pituitary gland and the autonomous nervous system (see diagram). In the case of continuous stress, this causes malfunctions within different organs. These include gastric and intestinal ulcers, cardiac, renal or pulmonary problems, muscular contractions etc.
The pituitary gland is capable of two reactions:
•a nervous reaction: liberation of ADH (vasopressin) which regulates the hydro-electrolytic equilibrium in the kidney.
•a humoral reaction (vascular) which is particularly important in stressful situations: the pituitary gland releases ACTH, which produces corticoids (stress hormones) by stimulation of the adrenal glands.
There are two sorts of corticoids:
1) mineralocorticoids (aldosterone) which regulate mineral (Na+, K+, Cl-) metabolism and blood pressure.
2) glucocorticoids: the most important in the case of stress and increases the production of cortisol significantly.
•slows the absorption of glucose by the cells and increases the concentration of blood glucose. It has a primordial role in the regulation of glucose metabolism.
•it also slows absorption of amino acids by muscular cells.
•cortisol increase has a depressing effect on anti-body producing cells (plasma cells as leukocytes and lymphocytes), leading to a heightened risk of inflammation and infection.
Prolonged stress may cause a permanent hormone release which can result in high blood pressure, gastric and/or intestinal ulcers, digestive, cardiac, cutaneous and pulmonary problems, higher risk of infection, loss of condition, lack of appetite etc. Also, lack of physical strength and resilience are stressful in themselves meaning that the situation becomes a vicious circle (see diagram).
How to stop this vicious circle and limit its consequences?
The horse’s routine and work are to be considered. Sport horses should always be offered antioxidants (D-Tox
) and probiotics (Biotics
) as well as courses of Equi’drink Immunotonic
Additionally, one should systematically:
•administer renal and hepatic cleansers and probiotics after a course of antibiotics, vaccinations or wormers: Equi’drink Drainage
•after changing yard or owner, let the horse get used to his environment. Horses get very attached to their environment and routine;
•for horses who travel often or for long periods of time, one should schedule periods of rest in order to avoid the stressful vicious circle mentioned above;
•in the event of fatigue and lack of appetite without a fever, a hepatic and renal cleanse alongside probiotics may be useful: Equi’drink Drainage
or Equi’drink Immunotonic
•if your horse yawns a lot with his head down, he may have high gastric acid levels: you may wish to follow a course of Thrive
: clay will absorb excess acidity. If this isn’t sufficient, you may wish to try GastriAid
(see also Digestion-Gastric Ulcers).
Always keep a watchful eye on your horse: you should pay attention to each change in his behaviour, attitude, appearance of his coat, appetite etc. If in doubt, please call your vet.